U.S. patent number 6,832,506 [Application Number 10/130,403] was granted by the patent office on 2004-12-21 for apparatus and method for measuring a property of a liquid.
Invention is credited to Andy Augousti, Michael Baker, Julian Mason, Norman McMillan, Stuart Smith.
United States Patent |
6,832,506 |
Mason , et al. |
December 21, 2004 |
Apparatus and method for measuring a property of a liquid
Abstract
An apparatus for use in characterising liquids by obtaining a
fingerprint of the liquid. This allows one to measure a property of
a liquid, and thereby distinguish between liquids. The apparatus
comprises means for directing acoustic energy at a sample of the
liquid, which is preferably in the form of a drop, and means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample. The drop may change in volume or shape
during the measurements, to derive additional properties of the
liquid. The apparatus and method of the invention are used in
distinguishing and analysing a variety of liquid samples.
Inventors: |
Mason; Julian (Kennington,
London, GB), Augousti; Andy (Yateley Hampshire,
Surrey, GB), McMillan; Norman (Carlow, County Carlow,
IE), Smith; Stuart (Blessington, County Wicklow,
IE), Baker; Michael (Carlow, County Carlow,
IE) |
Family
ID: |
11042166 |
Appl.
No.: |
10/130,403 |
Filed: |
September 23, 2002 |
PCT
Filed: |
November 16, 2000 |
PCT No.: |
PCT/IE00/00148 |
371(c)(1),(2),(4) Date: |
September 23, 2002 |
PCT
Pub. No.: |
WO01/36959 |
PCT
Pub. Date: |
May 25, 2001 |
Foreign Application Priority Data
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Nov 16, 1999 [IE] |
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S990960 |
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Current U.S.
Class: |
73/64.53;
73/590 |
Current CPC
Class: |
G01N
29/02 (20130101); G01N 29/2462 (20130101); G01N
2291/02818 (20130101) |
Current International
Class: |
G01N
29/02 (20060101); G01N 29/24 (20060101); G01N
029/00 () |
Field of
Search: |
;73/64.53,579,589,590,54.02,54.01 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Garber; Charles D.
Attorney, Agent or Firm: Whiteford, Taylor & Preston LLP
Maynard; Jeffrey C. Stone; Gregory M.
Claims
What is claimed is:
1. An apparatus for use in measuring a property of a liquid
comprising means for directing acoustic energy at a sample of the
liquid, an acoustic modulator for modulating the acoustic energy
independently of the resonant frequency of the sample, means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample as the acoustic energy is modulated, and
output means for providing an output based on said derived signal,
wherein the liquid sample is in the form of a drop which is
analysed dynamically during a change in drop volume, whereby the
output provides a characteristic measurement of the properties of
the liquid over a range of volumes based on varying acoustic energy
input parameters.
2. An apparatus according to claim 1, wherein the drop is formed
directly upon the means for directing acoustic energy at the
sample.
3. An apparatus according to claim 2, wherein the means for
directing acoustic energy comprises an acoustic source.
4. An apparatus according to claim 2, wherein the means for
directing acoustic energy comprises an acoustic guide attached to
an acoustic source, the drop being formed on an end of the acoustic
guide.
5. An apparatus according to claim 1, wherein the means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample comprises an acoustic detector, and wherein
the drop is formed directly upon the detector.
6. An apparatus according to claim 1, wherein the means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample comprises an acoustic detector having an
acoustic guide attached thereto, and wherein the drop is formed
directly upon an end of the guide.
7. An apparatus according to claim 1, wherein the liquid sample is
arranged to form pendant drops.
8. An apparatus according to claim 1, wherein the liquid sample is
arranged to form sessile drops.
9. An apparatus according to claim 1, wherein the means for
directing acoustic energy comprises a plurality of acoustic
sources.
10. An apparatus according to claim 9, wherein the signal produced
by the interaction with the sample is obtained by examination of
the loading effect on the driving signal to the acoustic
sources.
11. An apparatus according to claim 1, wherein the signal produced
by the interaction with the sample is obtained by comparing the
driving signal to the modulated signal received by one or more
detectors.
12. An apparatus according to claim 1, wherein the liquid sample is
in the form of a drop which is analysed statically for a fixed drop
volume.
13. An apparatus according to claim 1, wherein the liquid drop
undergoes a growth and release cycle, where one or more of a
succession of drops are allowed to drip from the end of an acoustic
drop head.
14. An apparatus according to claim 1, wherein the acoustic energy
is selected from acoustic radiation which is pulsed, continuous,
varying in frequency, amplitude or phase or otherwise
modulated.
15. An apparatus according to claim 1, wherein the means for
directing acoustic energy comprises an acoustic source, and a
liquid sample separated from the source by an intervening
medium.
16. An apparatus according to claim 15, wherein the acoustic energy
is launched at the unattached surface of the sample through said
medium.
17. An apparatus according to claim 16, wherein the means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample monitors two or more signals, including a
signal which penetrates the sample, and a signal based on the
acoustic field set up immediately outside of the sample.
18. An apparatus according to claim 1, wherein the means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample comprises an acoustic transduction
measurement system.
19. An apparatus according to claim 18, wherein the transduction
measurement system employs an electrical driving signal associated
with a source transducer and an electrical modulated signal
associated with a detector transducer, and wherein changes in the
driving signal and the modulated signal are used to deduce
properties relating to the liquid sample.
20. An apparatus according to claim 19, wherein a single transducer
acts as both source transducer and detector transducer.
21. An apparatus according to claim 1, further comprising means for
forcing movement or oscillation of the liquid sample during
acoustic measurements.
22. An apparatus according to claim 1, further comprising a tube
for containing the liquid sample, whereby the surface of the sample
liquid is a meniscus within said tube.
23. A method for measuring a property of a liquid, energy at a
sample of the liquid, modulating the acoustic energy being directed
at the liquid independently of the resonant frequency of the
sample, deriving a signal related to the interaction of the
acoustic energy with the liquid sample as the acoustic energy is
modulated, and providing an output indicative of a property of the
liquid based upon the said signal, wherein the liquid sample is in
the form of a drop which is analysed dynamically during a change in
drop volume and wherein the output provides a characteristic
measurement of the properties of the liquid over a range of volumes
based on varying acoustic energy input parameters.
Description
This invention relates to an apparatus and method for measuring a
property of a liquid. More particularly, it relates to the
characterisation of liquids by obtaining fingerprints for the
liquids, from which various properties can be derived.
There is a need for a range of techniques to analyse liquids to
detect differences between samples, such as in quality control,
detection of counterfeit goods, or analysis of tampering. The
invention also has as its aim the provision of an improved
technique for use in forensic analysis of liquids.
According to the present invention there is provided an apparatus
for use in measuring a property of a liquid comprising means for
directing acoustic energy at a sample of the liquid, and means for
deriving a signal related to the interaction of the acoustic energy
with the liquid sample.
The invention further provides a method for measuring a property of
a liquid comprising directing acoustic energy at a sample of the
liquid, deriving a signal related to the interaction of the
acoustic energy with the liquid sample, and determining a property
of the liquid based upon the said signal.
The liquid, which is preferably in the form of a drop, may be a
pure liquid, a mixture of liquids, a solution of a solid substance,
a suspension of a solid within a liquid or a colloidal suspension,
and the term "liquid" is used herein to signify all of these
possibilities.
The term "drop", as used herein, is defined as the interface that
is formed between a liquid and any other material or materials,
such as a solid, gas or liquid, under the force of the surface
tension of the interface usually, but not always, combined with the
force of gravity, acting on a particular geometrical arrangement of
said liquid and materials.
The drop can be formed using bioactive agents or radioactive
material.
The drop can undergo one or more phase changes during or at a
particular point in its growth cycle, and it can be contaminated
by, or dissolved, or evaporated into a surrounding medium.
Acoustic energy may be launched at the liquid sample from one or
more sources, and the signal produced by the interaction with the
sample can be obtained by various methods. One method is by
examination of the loading effect on the driving signal to the
acoustic source(s). A second is by comparing the driving signal to
the modulated signal received by one or more detectors. The
formation of the drop can take place directly upon an acoustic
source or at the end of an acoustic guide attached to a source
and/or a detector. Both configurations will henceforth be referred
to as an "acoustic drop head". The drop head can be arranged to
form either pendant or sessile drops.
The drop formed at the end of the acoustic drop head can be
analysed statically for a fixed drop volume or dynamically during
its growth and release cycle, where one or more of a succession of
drops are allowed to drip from the end of the acoustic drop head.
Thus one may analyse small volumes, or continuously monitor a
liquid by bleeding off sample droplets for analysis. The liquid may
also be allowed to evaporate from the drop formed under both static
or dynamic drop conditions.
The acoustic energy may be any acoustic radiation that can be
coupled into the drop, and it can be pulsed, continuous, varying in
frequency, amplitude or phase or otherwise modulated to facilitate
the particular analysis being performed. The acoustic energy can be
coupled directly into the drop using the acoustic drop head, which
is in direct contact with the test liquid or alternatively it can
be launched at the unattached surface of the drop through a medium
of different acoustic impedance. In such a case one may monitor two
or more signals--one is the signal that penetrates the drop, and
the other is based on the acoustic field set up immediately outside
of the drop. In some embodiments the source transducer may also act
as the detector transducer.
The signal related to the interaction of the acoustic energy and
the liquid sample can be measured using an acoustic transduction
measurement system. Any change in the driving signal from the
acoustic radiator and the modulated signal is then used to deduce
properties relating to the liquid under examination. The changes in
the electrical driving signal referred to above may arise from
variations in the acoustic impedance or geometry of the test
liquid, thereby "loading" the signal produced by the source
transducer. Changes in the acoustic signal may affect amplitude,
phase, frequency, reverberation time, harmonics etc.
The invention can be used to measure indirectly the following
properties of a liquid: Surface Tension Viscosity Acoustic
Impedance (i.e. density and the speed of sound within the test
liquid).
From these measurements, other properties of the test liquid ban be
determined, such as the concentration level of other species
contained within the liquid.
The acoustic energy may be optimised in terms of frequency and
power to set the drop of liquid into oscillation. Devices that
monitor the oscillation of the drop that is energised in this
fashion and simultaneously or subsequently monitor the drop by its
acoustic signal as described above are within the scope of this
invention. In addition, the invention includes the acoustic
analysis of drops that are stimulated into oscillation or movement
by any other means, such as mechanical energy, acoustic energy, an
external force, thermal energy or as the result of a chemical or
biological reaction
Embodiments of this invention are also possible where the surface
of the sample liquid is not a drop, but rather forms the meniscus
of a liquid within a tube, preferably a capillary tube.
Embodiments of the invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram of an apparatus for performing the
invention; and
FIGS. 2(a) to 2(d) illustrate alternative arrangements both for
launching acoustic energy at the drop and also the positioning of
detectors.
FIGS. 3 and 4 are the fingerprints derived using a method of the
invention in respect of two cola soft drinks; and
FIGS. 5 and 6 are the fingerprints derived using a method of the
invention in respect of two lagers.
In the figures the same reference numerals have been used for the
same or equivalent features.
Referring to FIG. 1, an acoustic drop head 10 includes a
cylindrical body 12 orientated with its axis substantially
vertical. The body 12 has a concave lower surface 14 and a central
axial bore 16 opening onto the surface 14. A liquid sample is
delivered to the acoustic drop head via a tube 18 communicating
with the bore 16, so that the liquid forms a pendant drop 20. The
delivery of the liquid can be via syringe, pump or using a constant
head of pressure, e.g. from a reservoir. Thus the drop 20 may be
static or it may be one of a succession of drops falling
intermittently from the body 12. The bore 16 in the body 12 can be
in any position provided there is a route to the drop-forming
surface 14. The cross-sectional profile of the drop-forming surface
14 is contoured to ensure repeatable drop shapes and drop
dimensions.
The drop head 10 also includes a disc 22 at the top of, and having
a greater diameter than, the body 12. The disc 22 is in intimate
contact with or is integral with, the body 12, and provides support
for an acoustic source 24 and an acoustic detector 26. In use,
acoustic energy from the source-24 is coupled into the drop head 10
and travels through the body 12 and into the drop 20. The
combination of drop head shape and drop geometry modulates the
acoustic signal which is then monitored by the detector 26 to
provide a corresponding signal.
As seen in FIG. 1, the lower end of body 12 is disposed coaxially
within the upper end of a vertical tube 28, the latter having
various side branches A to E which may be normal to the axis of the
tube (branches A, C, E) or inclined thereto (branches B, D). The
acoustic energy from a further source 30 (which can be positioned
at the end of branch A or B) is used to couple energy both into the
drop 20 and into the medium surrounding it. The modulated signal
can then be detected by a second detector 32 located at any of
branches C, D or E. In addition to this, the driving signal to the
acoustic sources 24, 30 is also monitored as this can be modulated
by the geometry of the drop 20. Detector 32 can also be used to
determine the acoustic energy radiating out of the drop from source
24.
In general there may be one or more acoustic sources each disposed,
like the source 26, on the drop head 10 itself or, like the source
30, spaced therefrom, and also one or more acoustic detectors
likewise disposed on the drop head or spaced therefrom.
The drive frequency to the acoustic source(s) may be varied over a
wide range, from tens of kilohertz to a few megahertz. The
electrical signal from the detector(s) is then plotted against time
to produce a graph called a tensiogram. The features in the
tensiogram are then used to determine the properties of the
liquid.
FIGS. 2(a) to 2(d) illustrate alternative arrangements both for
launching acoustic energy at the drop and also the positioning of
detectors. In FIG. 2(a), the body 12 of the drop head is generally
in the form of a truncated cone, thereby dispensing with the need
for the disc 22 (FIG. 1). FIG. 2(b) shows the same arrangement
inverted to form a sessile drop 20. FIG. 2(c) shows the source 24
and detector 26 on opposite sides of the body 12, while FIG. 2(d)
uses a combined acoustic source/detector 34. The drop heads of
FIGS. 2(c) and 2(d) may also be inverted to produce sessile
drops.
Other embodiments of the device include those where the foregoing
acoustic method of analysis of a liquid is combined with other
methods, such as optical analysis and capacitance-based techniques
that have been described elsewhere in work published by the present
applicants.
The invention can be used both for measuring the mechanical and
chemical properties of a liquid as detailed above, but also for
identification of an unknown liquid. Examples of applications of
such measurements will include on-line quality control
measurements, detection of fake materials, biomedical fluid
measurements, and reverse synthesis of particular formulations, es
well as any other are measurements on liquids are involved.
EXAMPLE
Experimental arrangement and procedure used to obtain
characteristic output data (fingerprints) for soft drinks and
beers.
The acoustic drop head used in this Example was designed to produce
pendant drops using the configuration in FIG. 1 (with the omission
of vertical tube 28 and its appendages) which was manufactured out
of a single section of brass. It was machined to produce a disc
section at the top (25 mm in diameter and 1.5 mm thick) and a
cylindrical shaft at the bottom (9 mm in diameter and 30 mm in
length). A domed recess was machined into the bottom end of the
cylindrical shaft to ensure proper wetting of the drop formation
surface.
A 2 mm diameter hole which acted as a fluid delivery passageway was
drilled through the axis of the probe head from the top of the disk
to the bottom of the shaft. Two ultrasonic transducers (10 mm in
diameter and 1 mm thick with an operating range from 20 KHz to 1
MHz) were soldered to the disk section by one of their metallised
end faces.
The centres of the transducers were 6.5 mm from the disk axis and
they were aligned such that the axes of both transducers and the
fluid passageway were parallel and coplanar. Since the end face of
each transducer was soldered directly to the brass disk this not
only provided a good acoustic coupling but also provided a common
electrical ground contact.
Test liquid was poured into a constant head tank, which then flowed
through 2 mm plastic tubing (with a 0.9 mm bore) to the acoustic
drop head. The plastic tube was inserted into the fluid passageway
of the probe head to the depth of 5 mm to provide a fluid tight
connection. The remaining face/electrical contact of the source
transducer was soldered to a lead connected to a Farnell signal
generator which had a frequency range from DC to 1 MHz. The
remaining face/electrical contact surface of the detector was used
as an input to an op-amp where the signal was both amplified and
rectified. The resulting DC signal was then applied to a 12 bit ADC
to permit data logging.
All liquids were degassed and allowed to reach room temperature
before being poured in to the header tank. Between each test tap
water was flushed through the system. After flushing, test liquid
was allowed to flow until equilibrium in the system was
reached.
This particular embodiment of this device was operated at a
frequency of 518,609 Hz and was used to test a number of liquids
and liquid mixtures. It was found that the device output was
extremely sensitive to variations in drop head geometry,
orientation, temperature, ultrasonic frequency and fluid flow rate,
so close environmental control and controlled fluid delivery is
required to achieve reproducible results.
FIGS. 3 and 4 show sample results obtained for the two cola drinks
Coca Cola (Trade Mark) and Diet Pepsi (Trade Mark) respectively.
The x and y axes are plotted with arbitrary units here, but by way
of scaling, a single drop took approximately 110 seconds to form.
The plots are both heavily featured, which is helpful for the
purposes of characterisation, since a greater number of features
means that there is more scope for variation from one liquid to
another.
Although the flow rates are slightly different, both plots
illustrate the repeatability of measurement within a particular
measurement run, with several complete drop growth cycles being
visible for each plot. The difference between the two traces is
very marked, and indeed this should be contrasted shortly with
FIGS. 5 and 6 for Heineken (Trade Mark) lager and Hofineister
(Trade Mark) lager respectively, which are very different from
these and each other in turn.
The largest factor in causing the variation between the Diet Pepsi
and the Coca Cola responses is the difference in the levels of
sugar. There are many peaks and troughs in each plot, and the
difference between the two is very marked.
FIGS. 5 and 6 show patterns which are generally different to those
of FIGS. 3 and 4, but are in some ways similar to one another, and
are perhaps indicative of a "lager" profile. However, the relative
depth and position of the peaks and troughs is quite different
between FIGS. 5 and 6, with some peaks that are present in the
Hofmeister plot being absent in the corresponding plot for
Heineken.
The invention is not limited to the embodiments described herein
which may be modified or varied without departing from the scope of
the invention.
* * * * *